Cryo-EM structures of plant Augmin reveal coiled-coil assembly, antiparallel dimerization, and NEDD1 binding
Microtubule branch nucleation, which builds complex microtubule networks in plants and metazoans, depends on the Augmin complex and NEDD1 to recruit and activate the γ-tubulin ring complex (γ-TuRC). Combining reconstitution, crosslinking mass spectrometry, and 3.7–7.3 Å cryo-EM, we built a complete de novo model of Arabidopsis Augmin, revealing long-range multi-coiled-coil interfaces that stabilize its 40-nm hetero-octameric fork-shaped architecture. The dual calponin homology domains at the V-junction adopt open and closed conformations for microtubule binding, Augmin undergoes antiparallel dimerization through conserved surfaces along its extended region, and the NEDD1 β-propeller binds directly inside the V-junction to enhance dimerization. These findings, validated by direct coupling and evolutionary covariation analyses, suggest that cooperativity between the CH domains and NEDD1 regulates Augmin’s V-shaped dual binding to the microtubule lattice, creating a platform for γ-TuRC recruitment and branched nucleation.